U.S. Pat. No. 5,295,662 discloses a diaphragm valve wherein a chamber within a valve body is divided by a flexible diaphragm into an operating chamber and a valve chamber. A fluid inlet passage terminates at an inlet opening in the bottom of the valve chamber. A valve seat is recessed within a groove in the bottom wall of the valve chamber and surrounds the inlet opening. A fluid outlet passage terminates at an outlet opening in the bottom wall of the valve chamber in a region outside the valve seat. A diaphragm operating mechanism selectively moves the diaphragm into contact with, or way from, the valve seat to selectively block or permit the flow of fluid from the fluid inlet passage to the fluid outlet passage. Because the valve seat is recessed in a groove in the bottom wall of the chamber, it is difficult to remove and replace in the event it is damaged or becomes worn. Furthermore, the bottom wall in which the valve seat is recessed may be damaged during the removal or replacement process in whch case the valve must be replaced or else the bottom wall machined.
The aforementioned patent also discloses a modified form of a diaphragm valve as described above. In the modified form the valve seat is not a separate element but instead comprises a ring-like projection on the bottom wall of the chamber which cooperates with the diaphragm to selectively block or permit fluid flow through the valve. If the valve seat in a valve of this type is damaged, it must be machined or the valve body replaced.